Engine compression release method and apparatus

ABSTRACT

The present invention comprises apparatus and methods for releasing internal combustion engine compression during cranking to reduce cranking effort and the size and weight of the starter motor and battery. It is particularly suitable for fuel conservation systems that stop the engine when the vehicle is stopped in traffic, and restart the engine when the driver steps on the accelerator petal, since such systems place heavy demands on the starter motor and battery. The apparatus provides a means for automatically shifting the valve gear such that exhaust and/or inlet valves are held slightly open during the intake compression strokes to reduce compression torque during initial cranking, and restoring the valves to normal operation before the first firing event. The method provides a sequence of steps executed by the engine electronic control module to control the compression release apparatus to carry out the engine starting process safely and reliably.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Ser. No. 61/687,835 filed May 2, 2012.

FIELD OF THE INVENTION

The present invention is related to methods and apparatus for temporarily reducing the compression pressure in reciprocating internal combustion engines during startup cranking, thereby reducing the cranking torque and energy required from the engine starting system. In particular, it is related to such methods and apparatus applicable to multi-cylinder vehicle engines that may be stopped and started frequently to reduce the fuel consumed while the vehicle is not moving.

BACKGROUND OF THE INVENTION

Significant fuel consumption savings may be gained in city driving by stopping the engine while the vehicle is stopped, and cranking and re-starting the engine automatically when the driver steps on the accelerator pedal. This repetitive cranking, however, places high torque and energy demands on the starting system, typically a battery powered electric motor, leading to larger and more costly batteries and motors than are required for less frequent use. Compression of air in the cylinders during the compression strokes is a major contributor to the torque and energy load, and partial release of air from the cylinders during the compression strokes during cranking is a well-known method of reducing cranking effort often used on small engines that need manual pull-start capability.

Typical prior art compression release systems incorporate a mechanism incorporated in the camshaft that opens the exhaust valves during a portion of the compression stroke to reduce the amount of fuel-air mixture trapped and compressed, thus reducing the compression and cranking effort. The exhaust valves reclose before ignition, since combustion pressure force on partially open exhaust valves would place unacceptably high stresses on the valve gear rather than carrying the force safely on the seat of the closed valve. The combustion and expansion of the reduced amount of fuel-air mixture is sufficient to increase the engine speed so that the rotary inertia of the crankshaft, flywheel and any other attached rotating mass powers subsequent compression strokes, leading to sustained engine operation. The compression release is disengaged manually or by a centrifugal mechanism for normal engine operation.

Contemporary vehicle engines offer new opportunities for compression release. They have computerized engine control modules that measure a number of parameters including crank angle, and control fuel delivery and ignition on a cycle by cycle basis to each cylinder. This allows the engine to be cranked up to starting speed with valves slightly open during the entire compression and expansion strokes to reduce compression, since the engine electronic control module may be used to turn off fuel delivery and/or ignition to prevent firing events that could otherwise damage the valve gear. When starting speed is reached, the valves are allowed to close fully and fuel and ignition are restored for normal sustained operation.

SUMMARY OF THE INVENTION

The present invention includes a compression release method for engine starting comprising:

Controlling the valve motion such that the exhaust and/or inlet valves remain slightly open during the compression and expansion strokes;

Disabling the fuel delivery and/or the ignition;

Cranking the engine to starting speed;

Controlling the valve motion such that the valves close completely; and

Enabling the fuel delivery and/or the ignition.

The invention further includes systems and apparatus for carrying out the controllable compression release method for engine starting comprising a cam and actuator or hydraulic pressure source that moves the rocker arm pivot relative to the cam lobe on command such that the associated engine valve does not fully close.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, in which like reference numbers indicate corresponding parts throughout the several views;

FIG. 1 is a view of a cam operated compression release mechanism in the normal engine operation mode;

FIG. 2 is a view of a cam operated compression release mechanism in the compression release mode;

FIG. 3 is a view of a hydraulically operated compression release mechanism in the normal engine operation mode;

FIG. 4 is a view of a hydraulically operated compression release mechanism in the compression release mode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The cam operated compression release mechanism according to the present invention is illustrated in FIG. 1 and FIG. 2. The cylinder head 100 incorporates a gas flow port 101 with a poppet valve 102 that serves to open and allow gas flow in or out of the cylinder volume or close to confine the gas in the cylinder during the compression and expansion strokes. The poppet valve is biased in the closed position by a spring 103 acting through the spring retainer 104. A rocker arm 105 pivoted on a lash adjuster 106 engages a rotating cam 107 with a lobe 108 work together to periodically open the poppet valve by pressing on valve stem tip 109. The spring 103 is compressed as the valve opens, and then expands to close the valve. In the normal operating mode shown in FIG. 1 the valve closes fully and seals against the valve seat 110 when the cam base circle 111 is in contact with the rocker arm 105, thereby preventing gas flow in or out of the cylinder. The lash adjuster 106 is an oil-filled device supplied by a pressurized engine oil gallery 112 inserted in a closely fitted cylindrical recess 113. It comprises a cylindrical body 114 with a flat end 115 that bears against the bottom of the recess 113 and a plunger 116 with a ball end 117 that forms the rocker arm pivot. The lash adjuster dynamically extends by taking in engine oil and contracts by leaking out oil to minimize free motion of the rocker arm relative to the cam and the valve stem tip, while allowing the valve spring 103 to seat the valve 102 firmly under all normal operating conditions. The oil leak rate is designed to reduce the lash adjuster length in response to relatively slow dimensional changes over a number of engine cycles, but at the same time to act as a nearly rigid and fixed length body over a single valve operating cycle. An internal check valve allows the lash adjuster to take in oil and extend much more quickly than it leaks and contracts.

The rotatable compression release cam 118 is positioned in a bore 119 adjacent to lash adjuster flat end 115, such that when it is rotated from the position shown in FIG. 1 to that shown in FIG. 2 the lash adjuster is moved partly out of the recess 113. The effect of rotating the compression release cam and moving the lash adjuster is to pivot the rocker arm 105 on the rotating cam 107, open the valve 102 and thereby release compression. In this mode the lash adjuster is constantly under spring load, and will tend to leak, contract, and bottom out. The compression release cam 118 is dimensioned to move the lash adjuster a distance sufficient to open the valve the necessary amount for compression release, plus allowances for lash adjuster leakage and contraction under load, engine tolerances, temperature effects and component wear. Piston modifications may be necessary to provide a safe amount of valve to piston clearance in some engines, since the valves do not close completely during compression relief and the maximum lift is increased. Valve springs are also compressed more, and this may be considered in the specifications.

The compression release cam may be rotated by a number of known means such as hydraulic, pneumatic or electrical rotary actuators, a lever and cylinder, or the like. It is important to avoid actuating the compression release during firing events to prevent engine damage, so power actuation and spring release is a preferred fail-safe arrangement to reduce the chance of inadvertent actuation. This in turn requires stored energy such as battery power, hydraulic pressure in an accumulator, or a vacuum reservoir for actuation. A compression release cam position sensor is desirable to signal the electronic control module that the valves are in fact restored to normal running operation before engine firing is initiated. A variety of devices including mechanical switches and optical or magnetic sensors or the like is suitable.

The hydraulically operated compression release mechanism according to the present invention is illustrated in FIG. 3 and FIG. 4. It is generally similar in arrangement and operation to the cam operated system, except that hydraulic pressure rather than a cam is used to shift the lash adjusters to release compression. A fluid-filled conduit 300 connects to the bottom of recess 113. When the fluid in conduit 300 is pressurized, pressure is applied to the lash adjuster flat end 115, and the lash adjuster is moved partly out of the recess 113 until it contacts the limit stop plate 301. As with the rotation of the compression release cam 119 to move the lash adjusters, the effect is to pivot the rocker arm 105 on the rotating cam 107 and open the valve 102 a controlled amount to release compression. Other parameters including the sequence of operations and the amount of lash adjuster movement are also similar.

Although in principle any pressurized fluid may be introduced into conduit 300 to move the lash adjuster, the engine lubricating oil is a convenient choice since it can leak around the lash adjuster and mingle with other lubricating oil in the lash adjuster oil gallery. The pressure required to move the lash adjuster in the range of 100 to 200 psi, higher than the 20 to 80 psi typical of engine lubricating pump pressures, but the volume is small, on the order of a cubic inch. A number of options may provide the intermittent oil pressure to move the lash adjusters and release compression. These include a battery powered pump switched on to provide the pressure and turned off to release it, or an engine or battery powered pump to charge an accumulator combined with a solenoid valve to control the oil flow. The accumulator and solenoid valve configuration offers the advantage of faster on-off response. A pressure sensor connected to conduit 300 that allows the electronic control module to determine when the compression release is active is useful to protect the engine and to carry out the automated starting procedure.

The compression relief apparatus described above enables the electronic control module to carry out a method for automatically restarting the engine that reduces the required torque and energy compared to starting with full compression. The method comprises the following steps:

Step 1. Detect the driver's intent to start the engine by measuring accelerator motion or another appropriate input signal.

Step 2. Turn on the compression release actuator such that the exhaust and/or inlet valves remain slightly open during the compression and expansion strokes.

Step 3. Measure compression release cam 119 position or pressure in conduit 300 to confirm that compression is released.

Step 3. Disable fuel delivery and/or the ignition.

Step 4. Crank the engine to starting speed and confirm speed.

Step 5. Turn off the compression release actuator such that the exhaust and/or inlet valves close normally during the compression and expansion strokes.

Step 6. Measure compression release cam 119 position or pressure in conduit 300 to confirm that compression is restored.

Step 7. Enable the fuel delivery and/or the ignition to begin self-sustained engine operation.

The method and apparatus of this invention enhance stop-start engine performance with modest changes to the engine and its valve gear. In particular, the valve gear dynamics in normal operation are unchanged, and ruggedness and reliability are not compromised. Further, the method assures proper automatic sequencing of the starting process, including measurement of parameters to confirm actions have taken place before proceeding to the next step, to optimize system performance and durability.

While the method and apparatus of the invention are described with reference to reducing torque and energy requirements for the engine starting process, it will be obvious to those skilled in the art that the invention is applicable to other purposes such as reducing compression-induced engine noise, vibration and harshness during engine shutdown. 

What is claimed is:
 1. A method for reducing the cylinder compression pressure of a rotating non-firing internal combustion engine on demand comprising adding a lift increment to the normal lift motion of at least one valve of at least one cylinder, wherein the lift increment is substantially independent of engine rotational position, thereby preventing complete valve closure and permitting gas flow form the cylinder during the compression stroke.
 2. The method of claim 1 wherein fuel delivery, ignition or both are disabled to achieve a non-firing condition in a rotating engine before adding the valve motion lift increment, and re-enabled in a rotating engine only after the valve motion lift increment is removed.
 3. The method of claim 1 wherein a sensing and control module is utilized to: Measure operating parameters, e.g. engine RPM, load, temperature, and valve motion lift increment status, and operator inputs including brake, accelerator or clutch status; Determine a requirement to reduce the cylinder compression pressure, and send a control command sequence comprising: Disable engine firing; and Add valve motion lift increment; or Determine a requirement to restore the cylinder compression pressure, and send a control command sequence comprising: Remove valve motion lift increment; Measure and confirm that the valve motion lift increment is removed; and Restore engine firing.
 4. A mechanism for adding a lift increment to the normal motion of at least one valve of at least one cylinder of an internal combustion engine by using an actuator to shift the position of the pivot of the rocker arm that opens the valve in a direction such that the valve remains open when the cam follower that actuates the rocker arm engages the base circle of the cam.
 5. The mechanism of claim 4 wherein the rocker arm pivot is the external ball element of the plunger of a conventional lash adjuster comprising a cylindrical body and plunger assembly mounted in a cylindrical pocket in the cylinder head structure; The actuator energized to shift the lash adjuster axially within the cylindrical pocket, thereby shifting the rocker pivot position closer to the cam such that the lift increment is added to the normal valve lift motion to initiate compression relief; and The actuator de-energized to return the lash adjustment to its original position to remove the lift increment to restore normal valve lift motion and eliminate compression relief.
 6. The mechanism of claim 5 wherein the actuator comprises a two-position shift cam controlling the lash adjuster axial position such that in a first position the lift increment is added to the valve motion and in a second position no lift increment is added, and a motor means for causing the shift cam to move between the first and second positions upon demand.
 7. The mechanism of claim 5 wherein the actuator comprises a conduit through which pressurized fluid is introduced to the cylindrical pocket to move the lash adjuster in the axial direction to a first position in which the lift increment is added to the valve motion, and through which the pressurized fluid is removed from the pocket to return the lash adjuster to a second position in which no lift increment is added, the mechanism further comprising a controlled fluid source connected to the conduit for introducing and removing the pressurized fluid upon demand.
 8. The mechanism of claim 7 wherein a mechanical stop limits the maximum axial motion of the lash adjuster under the influence of the pressurized fluid.
 9. The mechanism of claim 7 wherein the pressurized fluid delivered by the controlled fluid source is the lubricating oil circulating in the engine.
 10. The mechanism of claim 9 wherein the engine lubricating oil pressurized fluid is increased to a pressure higher than supplied to the engine components by a supplemental pump incorporated in the controlled fluid source.
 11. The mechanism of claim 10 wherein a hydraulic accumulator charged by the supplemental pump stores pressurized engine lubricating oil to move the lash adjuster in the axial direction, a controllable valve is connected between the hydraulic accumulator and the conduit, wherein the valve may be operated to introduce or remove the pressurized fluid upon demand. 